Extensive Frost Weathering Across Unglaciated North America During the Last Glacial Maximum. Issue 5 (1st March 2021)

• Record Type: Journal Article
• Authors: Marshall, J. A.; Roering, J. J.; Rempel, A. W.; Shafer, S. L.; Bartlein, P. J.
• Is Part Of: Geophysical research letters. Volume 48:Issue 5(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-03-01
• Subjects: critical zone -- frost weathering -- geomorphology -- LGM -- paleoclimate -- periglacial; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2020GL090305
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: In unglaciated terrain, the imprint of past glacial periods is difficult to discern. The topographic signature of periglacial processes, such as solifluction lobes, may be erased or hidden by time and vegetation, and thus their import diminished. Belowground, periglacial weathering, particularly frost cracking, may have imparted a profound influence on weathering and erosion rates during past climate regimes. By combining a mechanical frost‐weathering model with the full suite of Last Glacial Maximum climate simulations, we elucidate the meters‐deep magnitude and continent‐spanning expanse of frost weathering across unglaciated North America at ∼21 ka. The surprising extent of modeled frost weathering suggests, by proxy, the broad legacy of diverse periglacial processes. Complementing previous studies that championed the role of precipitation‐driven changes in Critical Zone evolution, our results imply an additional strong temperature control on surficial process efficacy across much of modern North America, both during glacial periods and modern climes. Plain Language Summary: Hillslopes and rivers are shaped by both modern and past climates. Climate and ecosystems drive how fast bedrock weathers, soil is produced, sediment moves downslope and rivers respond. We know that during glacial periods, unglaciated regions beyond the reach of ice sheets were much colder than today. By applying a frost‐weathering model (which predicts changes in porosity, and thus rock damage, due to growth of ice lenses) to Last Glacial Maximum paleoclimatic simulations, we demonstrate the surprising extent and magnitude of periglacial processes 21, 000 years ago across much of North America. No matter which paleoclimate simulation one chooses, the results point to just how extensive frost weathering processes were during the last glacial period, and by extension, multiple glacial periods of earth's history. Based on the widespread occurrence of glacial‐period frost weathering over meter‐scale depths, we suggest that past cold climates have had a significant impact on modern landscapes, both through lingering impact on subsurface pathways for water and thus chemical weathering, and the rock damage that contributes to the rate at which rock disaggregates into sediment and potential instability due to nonsteady rates of hillslope and river processes. Key Points: Frost weathering was extensive in unglaciated North America during the Last Glacial Maximum (LGM) LGM frost weathering and by association other periglacial processes occupied an area at least 3x greater than the mapped permafrost extent Inherited impacts from frost‐driven weathering during glacial periods has potential to influence modern Critical Zone function and form